A stretchable section is often included in a mooring cable or anchor rode for partly absorbing the stresses caused by wave actions on small boats, on buoys, or on similar floating structures. The elastic stretching of the rode helps to prevent damage to the craft or floating structure, as well as helping to prevent the loosening of its anchor. A stretchable segment is also sometimes included in a tow rope for dampening the shock of accelerating a floating object from rest, and for helping to even out the fluctuations in tension due to wave action during towing.
Generally, these stretchable segments include an elastomeric core surrounded by an extensible woven braid made from a synthetic polymer such as polyester or polyolefin.
A tension on the stretchable segment causes the braided outer layer of the rope to expand without resistance, while the inner elastic core stretches elastically and with increased resistance. Eventually, the braided outer layer reaches its maximum length, whereupon the tension load is transferred from the inner core to the outer braid, and the stretchable segment maintains its length until the tension is relieved.
An anchor rode is often partially wound on a capstan or around sheaves, and has shackles or knots at both ends thereof. Therefore, an anchor rode needs to be non-elastic along the segments thereof which are used for tying and along the segments susceptible to slippage and sharp bending. Hence, it is often desirable to make only a short segment of the anchor rode stretchable, as opposed to its full length. As a result, both ends of the stretchable segment are often submerged in a relatively harsh marine environment while in use, and are subject to both chemical and biological deterioration.
FIG. 1A illustrates a rode 10 being used to tether a ship 12 to an anchor 14, and FIG. 1B illustrates a rode 10 being used to tether a dock 18 floating on the surface 20 of an ocean, river, or lake, to the bottom 22 of the ocean, river, or lake. In both cases the rode 10 includes a stretchable segment 16 that remains entirely submerged while the rode 10 is in use.
Various methods are used to attach the elastomeric core to the braid at the ends of the stretchable segment 16. Typically, the elastomeric core emerges from the outer braid at each end, and is clamped, taped, and/or interwoven with the outer braid. An example is shown in FIG. 1C, where the elastomeric core 100 emerges through the surrounding outer braid 102 near one end, is folded back along the outside of the outer braid 102, and is interwoven through some of the loops 104 of the braid 102 to hold it in place.
As is illustrated in FIG. 1D, the ends of the stretchable segment 16 are terminated by loops 106 or other attachment fittings. In the figure, a steel thimble 106 is spliced to the woven braid 102. In other applications, a steel hook or other attachment fitting is spliced to the woven shield 102, or a “soft loop” is formed from the fibers of the woven shield itself. Typically, the non-elastic end portions of the stretchable segment 16 are wrapped with tape or encased in heat shrinkable tubing 108 to cover the joining region where both the end loop 106 and the elastomeric core 100 are attached to the woven braid 102. This is for aesthetic reasons, and also to protect the exposed section of the elastomeric core from abrasion and chafing, and from chemical and biological attack. However, tape and/or heat-shrinkable tubing 108 can only be applied to the short, non-elastic sections of the stretchable segment 16 near each end, since the application of tape or heat shrinkable tubing 108 to the elastic portion of the stretchable segment 16 would inhibit the free extension of the braid when the segment is stretched.
Due to its smooth surface and other material properties, the tape or heat-shrinkable tubing 108 is typically resistant to water and salt, and is not susceptible to undue amounts of marine attachment and growth. The synthetic material of the outer woven braid 102 is also typically impervious to attack from fresh or salt water, and the regular extensions and contractions of the braid inhibit the attachment and growth of marine life.
However, the braid extensions are greatest at the center of the stretchable segment, and least near the ends. Therefore, a region often exists near each end of a stretchable segment of a rode where the covering braid is not protected by tape or heat-shrinkable tubing 108, and yet does not undergo sufficient extension and contraction to inhibit the attachment and growth of marine life. This can lead to an unappealing appearance, as well as maintenance issues when the mooring cable is raised and the attached marine life must be removed and disposed of. In the worst case, it can even lead to degradation and eventual mechanical failure of the rode.
What is needed, therefore, is a protective covering system for end portions of a stretchable segment of a mooring rode that inhibits access of surrounding marine life to the end portions but does not inhibit expansion and contraction of the end portions.